The present application claims priority to Japanese Application No. P10-099021 filed Apr. 10, 1998 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to recording material, wherein heating with a heating means causes surface tension inclination, generating flow which causes the recording material to fly and be transferred onto a recording medium positioned opposing a transfer portion; and also relates to a recording method using this recording material.
2. Description of the Related Art
In recent years, in accordance with colorizing of video cameras, computer graphics, and so forth, there are increasing needs for color hard copies, not to mention black-and-white recording. With regard to such, color hard-copy printing methods which have been proposed include the dye dispersion thermal transfer method (or sublimation-type thermal transfer method), the melt thermal transfer method, the ink-jet method, the electro-photography method, the thermal-developing silver-salt method, and so forth. Of these, the dye dispersion thermal transfer method and ink-jet method can be classified as examples of methods whereby high-quality images can be easily output from relatively simple devices.
The dye dispersion thermal transfer method-uses an ink ribbon or sheet coated with an ink layer formed by dispersing a high concentration of transfer dye within an appropriate binder resin, and so-called photographic printing sheets which are formed by coating paper with dyeing resin which accepts the transferred dye. The ink ribbon or sheet is pressed against the thermal transfer sheet at a certain pressure, and a thermo-sensitive recording head (thermal head) applies heat from behind the ink ribbon or sheet, thus performing thermal transfer of transfer dye from the ink ribbon or sheet to the thermal transfer sheet, the amount of transfer dye being transferred according to the amount of heat applied to the dye receiving layer.
FIG. 16 shows the configuration of the area surrounding a thermal head of a printer using this dye dispersion thermal transfer method.
A thermal head 61 is positioned so as to oppose a platen roller 68, and an ink sheet 62 which has been formed by providing an ink layer 64 on a base film 63, for example, along with a recording sheet 65 formed by coating the surface of paper 66 with a dying resin layer (dye-accepting layer) 67, and run in the direction of the arrow A while being pressed against the thermal head 61 by the platen roller 68 which rotates in the direction of the arrow B in the Figure.
Then, the ink in the ink layer 64 selectively heated by the thermal head 61 according to the image to be printed is subjected to thermal dispersion into the dying resin layer 67 of the recording sheet 65 which has been heated by coming into contact with the ink layer 64, and transfer is carried out by dot pattern, for example.
A full-color image having continuous gradients can be obtained by repeating this operation for image signals resolved into the three primary colors of subtractive color mixture, i.e., yellow, magenta, and cyan. Much attention has been given to this dye dispersion thermal transfer method, as the printer can be reduced in size and maintenance thereof is simple, the printer has immediate availability, and images with quality rivaling that of silver-salt color photography can be obtained.
However, this method is problematic in that disposal of the ink ribbon or sheet results in massive amounts of discarded materials and high running costs, which has interfered with widespread use. This is also true for the melt thermal transfer method.
On the other hand, the ink-jet method is a method wherein droplets of recording material (hereafter referred to as xe2x80x9cinkxe2x80x9d) are discharged from nozzles provided to a printer head according to image information, using methods such as electrostatic gravity, continuous vibration generation (piezo method), thermal (bubble-jet method), and the like, as described in Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 5-217, and so forth, whereby the flying droplets of ink adhere to the printing paper or the like, thereby conducting recording.
Accordingly, printing can be performed on plain paper, and there are hardly any discarded items generated as with the case of using ink ribbons or the like, so running costs are low. This method is becoming widespread in recent years, since color images can be easily printed with the thermal method.
However, the principle of the ink-jet method makes concentration gradients in pixels difficult, and it has been difficult to realize images with quality rivaling that of silver-salt color photography in a short time, as can be with the above-described dye dispersion thermal transfer method.
That is to say, with the known ink-jet method, one droplet forms one pixel, so this principle makes concentration gradients within pixels difficult, and accordingly, high-quality images could not be realized. Also, pseudo-gradient representations with dithering using the high resolution of ink jets is being attempted, but image quality equal to that of the sublimation type thermal transfer method has not been obtained, and moreover, the transfer speed drastically drops when employing such methods.
In order to solve such problems, a method using so-called mist has been proposed in order to miniaturize the discharged droplets in the ink-jet recording method. This method can be generally divided into (1) the supersonic oscillation method, and (2) the satellite droplet method.
The former (1) is a method wherein mainly piezo oscillators are used to generate supersonic oscillation at the discharging portions, and minute droplets (ink mist) generated by the ink liquid striking against itself due to surface tension vibration caused by this oscillation are transferred. The latter (2) uses fine droplets generated as derivatives immediately following formation of main droplets for forming images, and with this method, the main droplets are not used in the image formation.
However, with the method (1), line heads are hard to form since miniaturization of piezo devices is generally difficult, and there is also the problem of slow speed, common to piezo devices. Also, localizing supersonic oscillations is difficult, making miniaturization even more difficult, and there is much interference from cross-talk, as well. Also, the method (2) requires complicated means such as charging the main droplets and bending the course thereof so the main droplets are not transferred to the recording paper. Such a method is actually restricted to the so-called continuous ink-jet recording method, and it is difficult to realize such at low costs.
The present Applicant has found an ink mist transfer method which solves the above problems.
This is a method wherein ink is caused to fly in the form of mist, using the collision force of ink owing to surface tension convection or the like generated by turning heating means on and off, and this mist is transferred onto a recording medium, thereby forming images of high quality. (refer to Japanese Patent Application No. 10-89030 (Date of Application: Apr. 1, 1998); hereafter referred to as xe2x80x9cInvention of Prior Applicationxe2x80x9d).
The Invention of Prior Application causes surface tension inclination at the surface of ink by means of resistance heating or laser beams, generating flow of ink (particularly surface tension convection or Marangoni flow) which causes the ink to fly, so ink can be caused to fly in the form of relatively large mist, this improving the transfer sensitivity per unit time. In this way, the Invention of Prior Application is a recording method which has excellent transfer sensitivity and printing speed.
With this method, providing heaters in high density can be easily realized by using known semiconductor processing techniques, and cross-talk can be prevented by providing appropriate structures on the heaters.
However, with a method which uses flow of the recording material as the driving force for causing ink to fly, as with the Invention of Prior Application, the ink must have physico-chemical qualities for generating sufficient surface tension convection; which had not been clarified in the Invention of Prior Application.
The present invention has been made in light of the above, and accordingly, it is an object of the present invention to provide recording material which effectively generates the above-described flow so as to improve transfer efficiency.
It is another object of the present invention to provide a recording method using this recording material.
As the result of careful study in order to solve the above-described problems, the present Inventor has found that, in a thermal transfer method wherein surface tension convection is used as the driving force to cause ink to fly, a suitable surface tension inclination can be brought about if the absolute value of the ink temperature coefficient is 0.07 dyn/cmxc2x7K or greater, whereby a sufficient amount of ink mist can be generated and images with sufficient color concentration can be formed.
That is, the present invention relates to a recording material, wherein heating with a heating means causes surface tension inclination, generating flow which causes the recording material to fly and be transferred onto a recording medium positioned opposing a transfer portion, the recording material having a surface tension temperature coefficient C represented by:
|C|xe2x89xa70.07(dyn/cmxc2x7K) (Expression 1)
This recording material shall hereafter be referred to as xe2x80x9crecording material according to the present inventionxe2x80x9d.
With the recording material according to the present invention, flow of recording material (particularly surface tension convection or Marangoni flow) owing to surface tension inclination causes the recording material to fly, and the recording material to be transferred to the recording medium has a surface tension temperature coefficient C represented the above in Expression 1, i.e., the recording material has an absolute value of surface tension temperature coefficient C of 0.07 dyn/cmxc2x7K or higher, so the surface tension of the recording material sharply responds to change in temperature, thus generating a sufficient surface tension inclination, consequently effectively generating the flow, thereby improving transfer efficiency.
The present invention also provides a recording method of heating recording material held in a transfer portion with a heating means to cause the recording material to fly and be transferred onto a recording medium positioned opposing a transfer portion;
wherein the recording material has a surface tension temperature coefficient C represented by:
|C|xe2x89xa70.07(dyn/cmxc2x7K) (Expression 1)
and wherein the heating causes surface tension inclination at the surface of the recording material, generating flow which causes the recording material to fly.
This recording method shall hereafter be referred to as xe2x80x9crecording method according to the present inventionxe2x80x9d.
With the recording method according to the present invention, heating recording material held in a transfer portion with a heating means causes the recording material to fly and be transferred onto a recording medium positioned opposing a transfer portion; wherein the recording material has a surface tension temperature coefficient C represented the above in Expression 1, i.e., the recording material has an absolute value of surface tension temperature coefficient C of 0.07 dyn/cmxc2x7K or higher, and wherein the heating causes surface tension inclination at the surface of the recording material, generating flow which causes the recording material to fly. So the surface tension of the recording material sharply responds to change in temperature, thus generating a sufficient surface tension inclination, consequently effectively generating the flow, thereby improving transfer efficiency.